1. Field of the Disclosure
The disclosure is directed to a pipeline apparatus and method, such as an apparatus and a method used to inspect or clean or tow an apparatus in an oil pipeline or a gas pipeline.
2. Discussion of the Related Art
It is known to use a pipeline inspection gauge (commonly referred to as a “pig”) to inspect or clean a pipeline, or to tow a tool through the pipeline. For example, the pig may be used to clean contaminants from an interior wall of the pipeline. The pig also may be used to detect defects, such as pitting, corrosion, a crack, or a weld abnormality, in a wall of the pipeline. These defects may be detected in a variety of ways, including through detection of magnetic flux leakage after developing and while maintaining a magnetic field in the wall of the pipeline. Alternatively, defects may be detected ultrasonically. The pig may also be used to inspect a geometry of the pipeline, or determine a location within the pipeline.
Pig launching and receiving portions are connected to the pipeline. As the names suggest, the pig launching portion is used to launch or introduce the pig into the pipeline, while the pig receiving portion receives the pig after the pig has traveled from the launching portion through the pipeline.
Specifically, a pressure differential between upstream and downstream sides of the pig moves the pig from the launching portion, through the pipeline, and into the receiving portion. The pig may include an interior channel, and a portion of the fluid (e.g., oil or gas) flowing through the pipeline also flows through the channel. The interior channel allows the fluid to flow through the pig while allowing a pressure on the upstream side of the pig to be greater than a pressure on the downstream side of the pig. Thus, the pig moves downstream as a result of the pressure differential.
There are disadvantages associated with traditional pigs. For example, as the pig moves from the launching portion, through the pipeline, and into the receiving portion, the pressure differentials on the upstream and downstream sides of the pig change. This is because, for example, in a pipe bend, a valve, a section of reduced diameter pipe or some other restriction, the pig may experience a greater resistance to motion than it would in a straight pipe. As the pressure differential between the upstream and downstream sides of the pig changes, the speed of the pig changes.
But, it is desirable to design the interior channel so that the pig moves through the whole pipeline at a speed suitable for cleaning or inspecting the wall of the pipeline, or towing a tool through the pipeline, without going too fast and compromising the quality of the inspection or damaging the pig or the pipeline, or without going too slow and becoming trapped in a restricted bore or radiused section of the pipeline. Further, when the pig is used to inspect the wall of the pipeline by detecting magnetic flux leakage or ultrasonically, the pig needs to move at a speed slow enough to effectively inspect the pipeline but fast enough to avoid becoming trapped in the pipeline. Thus, once the pig is in the pipeline, if the pig is moving too fast to perform the inspection, the pig can be slowed by decreasing the flow rate of the fluid flowing through the pipeline. But, decreasing the flow rate is undesirable because it results in a reduction of a quantity of the fluid transported through the pipeline. After moving through the pipeline, the pig needs to also move with sufficient speed to be fully received in the receiving portion.
Alternatively, it is known to use a pig that includes an interior channel with an outlet through which fluid flows at variable flow rates. As the flow rate of fluid flowing through the outlet varies, the pressure differential between the upstream and downstream sides of the pig, and thus the speed of the pig, changes. The pig suffers from disadvantages, however, including the need for complex arrangements of components to vary the flow rate of the fluid flowing through the outlet, and reduced reliability resulting from complex control equipment.